1. Field of the Invention
The present invention relates to lightning suppression attenuators. More particularly, the present invention relates to lightning suppression systems for reducing the magnitude of current of the lightning current wavefront as it moves along an electrical line following a lightning strike. More particularly, the present invention relates to lightning suppression systems for protecting the instrumentation and control systems associated with control or instrumentation cable.
2. Description of Related Art
Lightning conceivably may have provided humankind with a first source of fire, but lightning has otherwise been a destructive force throughout human history. Strategies and apparatus for reducing the likelihood of damage by lightning are fairly old, including, for instance, lightning rods that have been use for approximately 200 years. While the use of such rods and other precautionary steps and safety devices reduce the damage and injury that would otherwise result from lightning today, it remains an enormously dangerous natural phenomenon that claims hundreds of lives worldwide every year and destroys a substantial amount of property. Somewhat paradoxically, advances in other areas of technology have increased, rather than diminished, the damaged caused by lightning. This is because relatively low voltage and current levels can damage integrated circuits and other modem electronic components, with the result that many electronic devices are more susceptible to lightning damage today than ever before. Many devices to which microprocessors technology has been added are more susceptible to lightning damage as a result of such improvements. Additionally, lightning is capable of inducing substantial currents not only in electrical circuits directly struck by it but also in circuits located within the magnetic field induced by a nearby lightning strikes, giving each strike enormous destructive potential.
Whenever lightning strikes a tower, an enormous amount of damage is created. Typically, the electronic device at the top of the tower is completely destroyed by the lightning. Furthermore, the structure of the tower and other associated electronics at the top of the tower can become damaged. Repair efforts on the tower are often time consuming and expensive. Typically, complete replacement of the electronic device at the top of the tower is required. As such, it is very important to develop a device which resists or prevents lightning strikes.
One of the most common areas of lightning strikes are outdoor facilities, such as chemical processing plants and refineries. These facilities often have large water towers, chemical towers and cracking towers extending a large distance above the earth. Other towers are often employed in such facilities. Conventionally, these facilities includes various control instruments, such as actuators and monitoring equipment associated with the processing associated with such towers. The elevated structures in such facilities include suitable electronic devices which serve to transmit or receive information. Since lightning follows the path of least resistance on its way to the earth, these elevated facilities are very attractive to lightning. It is well known that lightning is particularly attracted to areas of positive ions and is repelled by areas of negative ions. Since the electronic devices at the tops of these elevated facilities often operate on AC power, an attractive source of positive ions is generated at the top of the tower. The lightning wavefront will travel along the instrumentation or control cable associated with such elevated structures so as to cause damage downstream of the cable to the monitoring and control instrumentation located within the facility.
Whenever lightning actually strikes such an elevated structure, an enormous amount of damage is created. Typically, the electronic device at the top of the elevated structure is completely destroyed by the lightning. Additionally, those controls and monitoring equipment that are connected to such instruments will also be destroyed by virtue of the lightning wavefront traveling along the instrumentation and control cable. The replacement and repair of such electronic devices either on the elevated structure or in the facility is very expensive and time consuming. In certain circumstances, the destruction of such equipment will necessitate a complete dumping of the chemicals in process within the refinery or chemical processing plant. As such, it is very important to develop a device which minimizes damage cost by lightning strikes to such elevated structures or traveling along the instrumentation and control cable associated with such instruments.
In the past, various patents have issued relating to devices for preventing or suppressing the affects of such lightning strikes. For example, U.S. Pat. No. 5,694,286, issued on Dec. 2, 1997 to the present inventors, describes a lightning protection device. This device has a tower which is grounded to the earth, an electronic device mounted onto an area adjacent to the top of the tower, and a negative ion production device electrically connected to the area of the top of the tower. The negative ion production device serves to produce solely negative ions around and over the electronic device. An auger rod engages the earth so as to be conductively connected to the earth. An electrically line serves to connect the auger rod to the tower. A shield member is connected to the tower and extends over the electronic device.
U.S. Pat. No. 5,844,766, issued on Dec. 1, 1998 to L. Miglioli, describes a lightning suppression system for tower mounted antenna systems. This system includes a directional coupler, a quarter-wavelength stub, a first cylindrical capacitor, a second cylindrical capacitor and a lightning suppression circuit. The lightning suppression circuit suppresses high voltage direct current and low frequency signals such as those produced by near lightning strikes.
It is an object of the present invention to provide a lightning suppression attenuator that effectively prevents lightning strikes from damaging equipment connected to instrumentation and control cables.
It is another object of the present invention to provide a lightning suppression attenuator that minimizes the magnitude of a lightning current as it moves along the instrumentation and control cable.
It is a further object of the present invention to provide a lightning suppression attenuator that minimizes the damaging effects of lightning.
It is still a further object of the present invention to provide a lightning suppression attenuator which is easy to install, relatively inexpensive and easy to manufacture.
These and other objects and advantages of the present invention will be come apparent from a reading of the attached specification and appended claims.
The present invention is a lightning suppression system comprising an instrument, a first cable having a first wire and a second wire connected to the instrument, an enclosure having an interior volume, a first coil positioned within the enclosure and electrically interconnected to the first wire, a second coil positioned within the enclosure and electrically interconnected to the second wire, and an electronic device electrically interconnected by a second cable to the first and second coils.
A conductive grit fills a portion of the enclosure around the first and second coils. In the preferred embodiment of the present invention, this conductive grit is steel shot. A rigid foam material can be affixed within the enclosure around the conductive grit and around the first and second coils. Each of the first and second coils has a central void with turns of wire extending around the central void. Each of the first and second coils has between 100 and 300 turns inclusive of wire extending around the central void.
A grounding rod is electrically connected by a conductive line to the enclosure. The grounding rod includes a central shaft, and a plurality of vanes extending radially outwardly from the central shaft. The central shaft and the plurality of vanes are formed of a conductive material. The conductive line connecting the grounding rod to the enclosure is a copper wire.
In one form of the present invention, the instrument can be a monitoring device and the electronic device is a display. In another form of the present invention, the instrument can be an actuator and the electronic device can be a controller. The first and second cables are generally of an identical structure. The second cable has a first wire interconnected to the first coil. The second cable having a second wire electrically interconnected to the second coil.